The present invention relates to surface mount electronic components, and more particularly, to surface mount reed switches.
By way of background, a conventional reed switch includes a pair of conductive switch contacts encapsulated within an elongated glass body which may have a cylindrical or rectangular cross-section extending along a longitudinal axis. The switch contacts are held in spaced-apart relationship to opposite sides of the longitudinal axis to define a carefully controlled gap therebetween. The ampere-turn or sensitivity rating of the reed switch corresponds to that gap. Typically, the switch contacts are defined at canted inner ends of a pair of conductive switch leads which extend along the longitudinal axis and out of the hermetically sealed glass body at opposed ends of the body.
The exposed outer ends of the leads may be electrically connected to conductive traces on a printed circuit (PC) board, for example, to interconnect with other electronic components. To this end, it has been conventional to form a 90.degree. downward bend in the exposed end of each lead so as to be directed towards the PC board and in a vertical plane (as viewed with the switch mounted to the PC board) defined along the longitudinal axis of the reed switch, i.e., the seating plane of the switch. The lead is thus in-line with the reed switch seating plane and extends well beyond the cylinder of the switch body to be receivable through a conductive hole formed in the board after which the lead may be soldered in place.
To more densely and closely pack electronic components on PC boards, through-holes in the PC board are eliminated. Instead, surface mount technology (SMT) has been developed. With SMT technology, a small conductive pad is provided on the surface of the PC board and the lead of the electronic component is soldered directly to that pad without extending through the PC board. To this end, the leads of the electronic components may be bent twice at oppositely directed 90.degree. angles along or parallel to the longitudinal axis to define a Z-shaped leg that extends along the seating plane of the reed switch. The lead is thus still in-line with the reed switch axis with the outermost end of the leg defining a flat or planar surface mount foot outside the cylinder of the switch body and oriented to extend along the seating plane of the switch. The surface mount foot rests directly in confronting relationship with the small contact pad on the surface of the PC board to make electrical contact therewith while also holding the electronic component above the board surface. Thereafter, the foot and contact pad are soldered together to secure the electrical connection.
Bending of the leads can place a stress on the associated electronic component. With respect to reed switches in particular, as the proximal end of each switch lead is bent close to the glass-to-metal seal to form the usual in-line surface mount foot at the distal end thereof, the result of stresses induced by bending may be seen at the inner end of the switch leads. Such stresses may adversely affect the hermetic sealing characteristics of the glass body or the predefined gap between the switch contacts causing erratic or inadequate performance of the reed switch.
In addition to the foregoing, because the in-line surface mount foot is typically defined along the length of the distal end of the lead itself, the width of the foot is usually relatively narrow. In reed switches, for example, where only two such feet are provided at extreme ends of the component body and are parallel to, but spaced from, the longitudinal axis thereof, the two narrow feet extend along the seating plane and so do not provide much stability to the reed switch resting on the PC board before it is soldered in place. An alternate SMT approach has been to provide an electronic component with a wide metal strip extending out of the body of the component, with the strip being bent into a C-shaped loop opening back towards the component in-line with the seating plane. While the bottom of the loop thus made provides a relatively wide surface mount foot, the use of such C-shaped in-line loops for reed switches continues to present bending stress problems and will not present any stability improvement due to the relatively thin wires used for reed switch leads.
One successful proposal to resolve the shortcomings set out above is shown in U.K. Patent Application Ser. No. 9503673.7 and U.S. Pat. No. 5,698,819. With the reed switch there-described, bending of the lead is eliminated by soldering a separate conductive pad element to the unbent lead to form a more stable surface mount foot without stressing the switch lead. While that construction is believed to be quite desirable, it does involve added manufacture and materials owing to the use of separate elements to define the surface mount feet.